JP2000340477A - Manufacture of junction wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a junction wafer which has high quality and high productivity. SOLUTION: The manufacturing method of a junction wafer includes a 1st stage thermal treatment to which, after an active wafer 2 and a base wafer 3 are joined, the junction unit is subjected in 1st thermal treatment atmospheric gas to form an oxide film 5 securely in a narrow gap 7 between the active wafer 2 and base wafer 3; and a 2nd stage thermal treatment to which the junction unit is subjected in 2nd thermal treatment atmospheric gas. The 2nd thermal treatment atmospheric gas is mixture of oxygen and hydrogen and has an oxidation rate faster than that of the 1st thermal treatment atmospheric gas. The oxide film 5 is built up quickly to a required thickness in the 2nd stage thermal treatment and a time necessary for the formation of the oxide film 5 can be reduced. The base wafer 3 is protected by the oxide film 5 from corrosion caused by etchant, so that the deterioration of the quality of the junction wafer can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a bonded wafer formed by bonding an active wafer and a base wafer.

[0002]

2. Description of the Related Art FIG. 2 is a schematic sectional view showing an example of a bonded wafer. Bonded wafer 1 shown in FIG.
Is an SOI (Silicon On Insulation) wafer,
The active wafer 2 and the base wafer 3 are joined via an oxide layer 4.

[0003] The bonded wafer 1 is manufactured as follows. For example, first, as shown in FIG. 3A, an active wafer 2 (silicon wafer) and a base wafer 3 (silicon wafer) are prepared, and as shown in FIG. An oxide layer 4 is formed on one or both surfaces of the base wafer 2 and the base wafer 3.
In the illustrated example, the oxide layer 4 is formed only on the active wafer 2.

Next, the surfaces of the active wafer 2 and the base wafer 3 are cleaned, and thereafter, the active wafer 2 and the base wafer 3 are bonded together as shown in FIG.

[0005] Then, the combined body of the active wafer 2 and the base wafer 3 is placed inside a heat treatment chamber (not shown), and the combined body is heated to, for example, 1000 to 1200 ° C. to perform a heat treatment. By this heat treatment, the bonding strength between the active wafer 2 and the base wafer 3 is increased. Also,
In this heat treatment step, an atmosphere gas containing an oxygen gas is supplied into the heat treatment chamber, and as shown in FIG. 3D, an oxide film 5 is formed on the surface of the assembly by the atmosphere gas. You.

After the heat treatment step is completed, the combined body is taken out of the heat treatment chamber.

By the way, as shown in the sectional view of the wafer 2 (3) in FIG. 4, the side end surfaces 2a (3a) of the active wafer 2 and the base wafer 3 are rounded, and
Each peripheral edge region 2b of the active wafer 2 and the base wafer 3
(3b) has a very small inclination θ in the direction in which the thickness of the wafer becomes thinner (a part having this small inclination is called “sag” here). For this reason, a non-bonded region (unbonded region) X as shown in FIG. 5A is generated in the peripheral region between the active wafer 2 and the base wafer 3 in the bonded body. .

[0008] As described above, if the unbound region X is present in the peripheral end region of the bonded body, the following problem may occur. In other words, in a step subsequent to the heat treatment step, the active wafer 2 is reduced to a predetermined thickness by using a polishing technique. If there is a region X, the active wafer 2
During the polishing, problems such as peeling of the active wafer 2 and the base wafer 3 from the unbonded region X and chipping of the peripheral end portion of the active wafer 2 occur.

Therefore, after the heat treatment is completed, FIG.
(E), the unbonded region X of the active wafer 2
Is removed by grinding and etching. In the etching step, the oxide film 5 formed on the surface of the base wafer 3 functions as a protective film for protecting the base wafer 3 from an etchant.

Thereafter, the active wafer 2 is polished to a thickness specified by the specification, for example, and then polished to complete the bonded wafer 1 as shown in FIG. . The oxide film 5 formed on the surface of the base wafer 3 may be removed or may remain as it is.

[0011]

If the thickness of the oxide film 5 formed on the surface of the base wafer 3 in the heat treatment step is small, the oxide film 5 becomes a protective film of the base wafer 3 in the etching step. Cannot be performed, the surface of the base wafer 3 is etched, and the thickness of the base wafer 3 is rapidly changed as shown in FIG. An abnormal shape occurs.

In order to prevent the occurrence of the step, the oxide film 5
For example, in the heat treatment step, the atmosphere gas in which the nitrogen gas is mixed with the oxygen gas at a mixing ratio such that the nitrogen gas amount becomes 5 when the oxygen gas amount is set to 1 is considered. When used, since the formation rate (oxidation rate) of the oxide film 5 is very slow, it takes a very long time, for example, several tens of hours, until the thickness of the oxide film 5 reaches a desired thick film thickness. This causes a problem of lowering the productivity of the bonded wafer.

Therefore, it is conceivable to use a gas having a high oxidation rate. However, when a gas having a high oxidation rate is used, the following problem occurs.

As described above, there is sagging in each peripheral end region 2b (3b) of the active wafer 2 and the base wafer 3.
Due to the sagging, a gap 7 is formed between the active wafer 2 and the base wafer 3 in the combined body as shown in FIG. This gap 7 is the active wafer 2
This is a very narrow gap such that the distance d between the substrate and the base wafer 3 is 1 μm or less.

Since the gap 7 is very narrow, it is difficult for the atmosphere gas to enter the gap 7 in the heat treatment step. Before the formation of the oxide film 5, the oxide film 5 is formed so as to block the entrance of the gap 7, as shown in FIG. For this reason, there is a problem that the atmosphere gas cannot enter the gap 7 and the oxide film 5 is not formed.

As described above, if the oxide film 5 is not formed in the gap 7, a portion of the base wafer 3 that is exposed to the etchant is formed in the above-mentioned etching step, and as shown in FIG. Base wafer 3
The portion exposed to the etching solution is etched, and a groove 8 is formed in the peripheral end region 3b of the base wafer 3, which causes a problem that the quality of the bonded wafer 1 is deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to form an oxide film capable of reliably protecting a base wafer in an etching step, and to form the oxide film. It is an object of the present invention to provide a method for manufacturing a bonded wafer capable of reducing the time required for performing the bonding.

[0018]

In order to achieve the above-mentioned object, the present invention provides means for solving the above-mentioned problems with the following constitution. That is, a first aspect of the present invention is a method of manufacturing a bonded wafer in which an active wafer and a base wafer are bonded to each other, in a state where a combined body of the active wafer and the base wafer is disposed inside the heat treatment chamber. Performing a first-stage heat treatment using an ambient gas to form an oxide film on the surface of the combined body;
A second-stage heat treatment is performed using a second heat treatment atmosphere gas in which the oxide film formation speed is higher than the oxide film formation speed in the second heat treatment step, so that the oxide film of the composite is grown. As described above, the above-described means is achieved by a configuration in which heat treatment is performed in at least two stages using heat treatment atmosphere gases having different oxidation rates to form an oxide film on the surface of the combined body.

According to a second aspect of the present invention, there is provided the configuration of the first aspect, wherein the first heat treatment atmosphere gas is a gas having a lower oxide film formation rate than the gas containing only oxygen gas. The atmosphere gas for use is characterized in that the oxide film is formed at a higher rate than the gas containing only oxygen gas.

According to a third aspect of the present invention, there is provided the structure of the first or second aspect, wherein the first heat treatment atmosphere gas is a mixed gas of oxygen gas and an inert gas, and the second heat treatment atmosphere gas is It is characterized by being a mixed gas of oxygen gas and hydrogen gas.

According to a fourth aspect of the present invention, the heat treatment of the first stage and the heat treatment of the second stage are continuously performed, and the heat treatment of the first stage and the second stage are performed. When the transition to the heat treatment is performed, the mixing ratio of the inert gas to the oxygen gas in the first heat treatment atmosphere gas is varied continuously or stepwise.

According to a fifth aspect of the present invention, there is provided the first, second or third aspect.
Alternatively, the bonded wafer according to the fourth aspect of the present invention is characterized in that the bonded wafer is an SOI wafer formed by bonding an active wafer and a base wafer via an oxide layer.

In the invention having the above structure, in the heat treatment process after the bonding of the active wafer and the base wafer, the active wafer and the base wafer are exposed by, for example, a first heat treatment using a first heat treatment atmosphere gas. An oxide film is formed on the surface. At this time, the first heat treatment atmosphere gas is also introduced into a very narrow gap between the active wafer and the base wafer to reliably form an oxide film.

Thereafter, a second heat treatment is performed using a second heat treatment atmosphere gas. The second heat treatment atmosphere gas has a higher oxidation rate than the first heat treatment atmosphere gas. In the second stage heat treatment, the second heat treatment atmosphere gas has a higher oxidation rate than the first stage heat treatment. An oxide film on the surface of the conjugate is grown.

As described above, the oxide film is formed by at least two-stage heat treatment using the atmosphere gases having different oxidation rates, so that the oxide film is formed even in a very narrow gap between the active wafer and the base wafer. And an oxide film having a film thickness capable of reliably protecting the base wafer in the etching step can be formed in a short time.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

The bonded wafer in this embodiment has the same configuration as that of the bonded wafer shown in FIG. 2 and is manufactured by a process substantially similar to the manufacturing process described above. The heat treatment process in the manufacturing process is a process unique to this embodiment. The other configuration is the same as that of the above-described conventional example. The same components as those of the conventional example are denoted by the same reference numerals, and the description thereof will not be repeated.

In the characteristic heat treatment step of this embodiment, the combined body of the active wafer 2 and the base wafer 3 is heat-treated in two stages. That is, after the active wafer 2 and the base wafer 3 are combined and integrated, the combined body is placed in a heat treatment chamber (not shown), and first, the first stage heat treatment is performed. In the first heat treatment, the bonded body is heated to, for example, 1000 ° C. to 1200 ° C. to increase the bonding strength between the active wafer 2 and the base wafer 3, and
The first heat treatment atmosphere gas is supplied to the heat treatment chamber to form an oxide film 5 on the surface of the combined body of the active wafer 2 and the base wafer 3.

[0029] The first heat treatment atmosphere gas may be a predetermined mixture ratio of oxygen gas and inert gas (for example, when the oxygen gas amount is 1, the nitrogen gas amount is 3).
And a gas whose oxidation rate (formation rate of the oxide film 5) is lower than when only oxygen gas is used.

In the first heat treatment, as described above, the heat treatment is performed using an atmosphere gas whose oxidation rate is lower than that in the case where only oxygen gas is used.
As shown in (a), the oxide film 5 can be reliably formed even in the very narrow gap 7 between the active wafer 2 and the base wafer 3. In other words, since the oxidation rate is slow, it takes time until the entrance of the gap 7 is closed by the oxide film 5, so that the first heat treatment atmosphere gas is surely introduced into the interior of the gap 7. As a result, the oxide film 5 can be formed also in the gap 7.

When such a first-stage heat treatment is performed, if the predetermined switching condition is satisfied, the first-stage heat treatment is switched to the second-stage heat treatment. For example, the time required from the start of the first-stage heat treatment to the time when the gap 7 is filled with the oxide film 5 is determined in advance by experiments, calculations, and the like, and after the start of the first-stage heat treatment. When the obtained time (for example, one and a half hours) has elapsed, it is determined that the switching condition has been satisfied, and the heat treatment is switched from the first stage to the second stage heat treatment.

In this embodiment, the atmosphere gas supplied to the heat treatment chamber is changed from the first heat treatment atmosphere gas to the heat treatment chamber while the combined body is continuously heated to 1000 to 1200 ° C. after the first heat treatment. By switching to the second heat treatment atmosphere gas, the first heat treatment is switched to the second heat treatment.

The second heat treatment atmosphere gas is a gas obtained by mixing an oxygen gas and a hydrogen gas at a predetermined mixing ratio. When the oxygen gas and the hydrogen gas are separately supplied to the heat treatment chamber, And hydrogen gas are reacted in advance by heating to form steam gas and then supplied to the heat treatment chamber, and any of these methods may be employed. The second heat treatment atmosphere gas is a gas whose oxidation rate is faster than the case where only oxygen gas is used, and is naturally a gas whose oxidation rate is faster than the first heat treatment atmosphere gas.

In the heat treatment of the second stage, the oxide film 5 formed on the surface of the combined body is grown at an oxidation rate faster than that of the heat treatment of the first stage as shown in FIG. . Then, when the predetermined heat treatment termination condition is satisfied, the second stage heat treatment is terminated. For example,
The thickness of the oxide film 5 capable of functioning as a protective film of the base wafer 3 is determined by experiments or the like. The oxide film 5 of the base wafer 3 is formed by using the second heat treatment atmosphere gas. The time required to grow the film to the above-determined film thickness is determined in advance by experiments and the like.
When the above-described time (for example, one and a half hours) has elapsed since the start of the heat treatment in the second stage, it is determined that the heat treatment end condition has been satisfied, and the heat treatment in the second stage is ended.

As described above, in this embodiment, the heat treatment of the combined body is performed in two stages using two kinds of atmosphere gases having different oxidation rates.

According to this embodiment, in the first heat treatment, the first heat treatment atmosphere gas is used, and the oxide film 5 is formed on the surface of the combined body at a slow oxidation rate. Atmospheric gas can be sufficiently supplied to the deep portion of the gap 7 between the base wafer 3 and the base wafer 3, and the oxide film 5 can be formed in the gap 7 reliably.

In addition, after the oxide film 5 is formed in the gap 7, the heat treatment in the first stage is shifted to the heat treatment in the second stage, and the oxidation rate is increased to grow the oxide film 5. In addition, the time required for growing oxide film 5 to a thickness that can function as a protective film for base wafer 3 can be reduced, and the productivity of bonded wafer 1 can be improved.

As described above, in the heat treatment process characteristic of this embodiment, the oxide film 5 is formed also in the gap 7 and the oxide film 5 formed on the surface of the base wafer 3 is etched. Since the thickness is such that the base wafer 3 can be sufficiently protected from the liquid, the surface of the base wafer 3 is surely protected by the oxide film 5 in the etching step after the heat treatment step, and the (FIG. 1) As shown in c), it is possible to provide the bonded wafer 1 having no irregularities in the shape of the step, the groove 8 and the like, and it is possible to easily improve the quality of the bonded wafer 1.

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various embodiments. For example, in the above embodiment, the first heat treatment atmosphere gas is a mixed gas of oxygen gas and nitrogen gas, and the second heat treatment atmosphere gas is a mixed gas of oxygen gas and hydrogen gas. The atmosphere gas for heat treatment may be a gas capable of increasing the oxidation rate more than the atmosphere gas for the first heat treatment. In other words, the first atmosphere gas for the heat treatment is the second atmosphere gas.
The first and second heat treatment atmosphere gases are not limited to the mixed gas described in the above-described embodiment. For example, one of the first heat treatment atmosphere gas and the second heat treatment atmosphere gas may be a gas containing only oxygen gas. However, when the second heat treatment atmosphere gas is only oxygen gas, the oxidation rate is slightly lower than when the second heat treatment atmosphere gas is a mixed gas of oxygen gas and hydrogen gas.

Since the oxidation rate increases as the mixing ratio of nitrogen gas to oxygen gas decreases,
When the first heat treatment atmosphere gas is a mixed gas of oxygen gas and nitrogen gas, for example, at a mixture ratio where the nitrogen gas is smaller than the mixture ratio of oxygen gas and nitrogen gas in the first heat treatment atmosphere gas. A gas in which oxygen gas and nitrogen gas are mixed may be used as the second heat treatment atmosphere gas.

Further, since the oxidation rate becomes slower as the mixing ratio of hydrogen gas to oxygen gas becomes smaller, when the second heat treatment atmosphere gas is a mixed gas of oxygen gas and hydrogen gas, for example, A gas obtained by mixing the oxygen gas and the hydrogen gas at a mixing ratio in which the hydrogen gas is smaller than the mixing ratio of the oxygen gas and the hydrogen gas in the second heat treatment atmosphere gas may be used as the first heat treatment atmosphere gas.

Further, in the above embodiment, the heating temperature of the combined body in each of the first and second heat treatments is 1
Although the heating temperature was from 000 ° C. to 1200 ° C., the heating temperature is appropriately set, and is not limited to the heating temperature shown in the above embodiment. In the above-described embodiment, the heating temperatures of the first and second heat treatments are substantially equal, but the heating temperatures of the first and second heat treatments are appropriately set as described above. It is set and may be different.

Further, in the above embodiment, the first-stage heat treatment and the second-stage heat treatment are continuously performed in the same heat treatment chamber. However, for example, the first-stage heat treatment is completed. At the same time, the heat treatment of the first stage and the heat treatment of the second stage may be discontinuously performed, such as temporarily stopping the heating of the combined body and then starting the heat treatment of the second stage. A heat treatment chamber for performing the first stage heat treatment;
By separating the heat treatment chamber for performing the second-stage heat treatment, the first-stage heat treatment and the second-stage heat treatment may be performed discontinuously.

Furthermore, in the above embodiment, when the heat treatment of the first stage is shifted to the heat treatment of the second stage, the atmosphere gas for the first heat treatment is rapidly switched to the atmosphere for the second heat treatment. However, the atmosphere gas for the first heat treatment may be gradually shifted to the second atmosphere gas for the heat treatment. For example, during a transition period from the first heat treatment to the second heat treatment, the mixture ratio of nitrogen gas to oxygen gas in the first heat treatment atmosphere gas is continuously or stepwise reduced. The supply of the nitrogen gas is stopped when the mixture ratio of the nitrogen gas to the oxygen gas becomes smaller than a predetermined value. At the same time as the supply of the nitrogen gas is stopped or after the supply of the nitrogen gas is stopped, the mixing of the oxygen gas with the hydrogen gas is started. The mixing ratio of the hydrogen gas to the oxygen gas increases continuously or stepwise from the start of the supply of the hydrogen gas toward the set mixing ratio of the second heat treatment atmosphere gas. As described above, the atmosphere gas for the first heat treatment may be gradually shifted to the atmosphere gas for the second heat treatment.

Further, in the above embodiment, the heat treatment was performed on the combined body in two steps.
The heat treatment may be performed in multiple stages or more. The number of heat treatment stages is appropriately set, and a heat treatment atmosphere gas having a different oxidation rate is used for each heat treatment in each stage.

Further, in the above-described embodiment, sagging occurs in each of the peripheral end regions 2b (3b) of the active wafer 2 and the base wafer 3, but the present invention is, of course, applicable to the active wafer 2 and the base wafer 3.
The present invention can also be applied to a case where there is no sagging in one or both peripheral end regions of the base wafer 3 and the base wafer 3.

Further, in the above embodiment, the SOI wafer in which the active wafer 2 and the base wafer 3 are bonded via the oxide layer 4 has been described as an example. Can also be applied to a direct-bonding-type bonded wafer that directly bonds the same, and in this case, the same effect as in the above-described embodiment can be obtained.

[0048]

According to the present invention, an oxide film is formed on the surface of the combined active wafer and base wafer by performing heat treatment in at least two stages using atmospheric gases having different oxidation rates. By the stage heat treatment,
For example, an oxide film is formed on the exposed surface of the above-mentioned combined body, and an oxide film is also formed in a very narrow gap in the peripheral edge region between the active wafer and the base wafer. The formed oxide film is removed from the first
Since the oxide film can be grown at an oxidation rate faster than the heat treatment at the stage, the oxide film is grown to a thickness that can reliably protect the base wafer from the etchant in the etching process after the heat treatment process. The time required for the bonding can be reduced, thereby improving the productivity of the bonded wafer.

In addition, as described above, an oxide film is surely formed even in a narrow gap in the peripheral edge region between the active wafer and the base wafer. Therefore, in the etching step after the heat treatment step, the oxide film The base wafer can be reliably protected from the etching solution, the abnormal shape of the bonded wafer can be prevented, and the quality of the bonded wafer can be improved.

The first atmosphere gas for heat treatment is a gas having a lower oxide film formation rate than the gas containing only oxygen gas.
The first heat treatment atmosphere gas is a gas having a higher oxide film formation rate than the oxygen gas only gas, and the first heat treatment atmosphere gas is a mixed gas of an oxygen gas and an inert gas.
In the case where the second heat treatment atmosphere gas is a mixed gas of oxygen gas and hydrogen gas, the oxide film is more reliably formed in a very narrow gap between the active wafer and the base wafer by the first heat treatment. Further, the growth of the oxide film can be further accelerated by the second heat treatment.

In the transition from the first heat treatment to the second heat treatment, the direction in which the mixing ratio of the inert gas to the oxygen gas in the first heat treatment atmosphere gas is continuously or stepwise reduced. When the atmosphere gas for the first heat treatment and the atmosphere gas for the second heat treatment are suddenly switched, the first atmosphere gas for the heat treatment and the second atmosphere gas for the second heat treatment are changed. If it reacts excessively,
By gradually shifting from the first heat treatment atmosphere gas to the second heat treatment atmosphere gas, an excessive reaction between the first heat treatment atmosphere gas and the second heat treatment atmosphere gas can be prevented.

Even if the bonded wafer is an SOI wafer, the quality of the SOI wafer can be improved and the productivity of the SOI wafer can be easily increased as described above.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically illustrating an example of a bonded wafer.

FIG. 3 is an explanatory view showing an example of a manufacturing process of a bonded wafer.

FIG. 4 is a cross-sectional view schematically showing one example of a peripheral end portion of a wafer.

FIG. 5 is an explanatory diagram showing a conventional problem.

FIG. 6 is an explanatory view showing a conventional problem.

[Explanation of symbols]

 Reference Signs List 1 bonded wafer 2 active wafer 3 base wafer 4 oxide layer 5 oxide film 7 gap

Claims (5)

[Claims] 1. A method for manufacturing a bonded wafer in which an active wafer and a base wafer are bonded to each other, wherein a first heat treatment atmosphere gas is provided in a state where a combined body of the active wafer and the base wafer is disposed inside the heat treatment chamber. Performing a first-stage heat treatment using an oxide film to form an oxide film on the surface of the combined body, and then forming an oxide film at a speed lower than the oxide film formation speed in the first-stage heat treatment process. Heat treatment in at least two stages using heat treatment atmosphere gases having different oxidation rates, such as performing a second heat treatment using a second heat treatment atmosphere gas which is faster to grow an oxide film of the above-mentioned combination. And forming an oxide film on the surface of the bonded body by performing the method described above. 2. The first heat treatment atmosphere gas is a gas having a lower oxide film formation speed than a gas containing only oxygen gas.
2. The method for manufacturing a bonded wafer according to claim 1, wherein the second heat treatment atmosphere gas is a gas having a higher oxide film formation rate than a gas containing only oxygen gas. 3. The atmosphere gas for a first heat treatment is a mixed gas of an oxygen gas and an inert gas, and the second atmosphere gas for a heat treatment is a mixed gas of an oxygen gas and a hydrogen gas. The method for manufacturing a bonded wafer according to claim 1. 4. A first heat treatment and a second heat treatment are continuously performed, and when the heat treatment is shifted from the first heat treatment to the second heat treatment, a first heat treatment is performed. 4. The method for manufacturing a bonded wafer according to claim 3, wherein the mixing ratio of the inert gas to the oxygen gas in the atmospheric gas is varied continuously or stepwise. 5. The bonded wafer according to claim 1, wherein the bonded wafer is an SOI wafer formed by bonding an active wafer and a base wafer via an oxide layer. Manufacturing method of bonded wafer.